Engines require more fuel when cold, that was the purpose of the Choke on a carbureted
engine.
Fuel injected engines use the computer and an ECT sensor, the ECT(engine coolant temp) sensor is a TWO wire sensor, not to be confused with the 1 wire sender used for the dashboard temp gauge.
The ECT sensor tells the computer if engine is cold or warm, and computer adjusts fuel richness accordingly.
The ECT is a simple resistance sensor so easy to test with an OHM meter, low OHMs cold, high OHMs warm.
But not sure I would call the result of a bad ECT sensor Flooding, poor MPG and rich yes, but no stalling.
Since an engine needs more fuel when cold, a stuck open injector might not be noticed until engine warms up.
Leaking or non-functioning Fuel Pressure Regulator(FPR) might do the same.
FPR has a rubber diaphragm that can crack with age, it also has a vacuum line direct to the intake, if diaphragm is cracked then fuel can be sucked into the engine, again cold engine might like the extra fuel but not so a warm engine.
Non-function FPR might cause the fuel pressure in the system to be higher than 40psi, so when computer opens the injectors more fuel than expected is going past, again cold engine might like the extra fuel but not so a warm engine.
Bad O2 sensors can cause rich mix but I wouldn't call that Flooding either, computer has limits on how rich it will run the engine.
My money would be on injectors or FPR.
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